1. Field of The Invention
The process presented pertains to the manufacture of cellular foam and particularly to a post treatment of polyurethane foam for greater structural consistency when formed on a continuous production line.
2. Description of the Prior Art And Objectives of The Invention
Polyurethane and other cellular foams are generally formed in continuous or batch processes whereby liquid chemical components are mixed and the reaction results in a foam of substantially desired density and compression qualities. For production of a polyurethane foam, a polyol, water and diisocyanate are reacted in the presence of a catalyst. In many commercial operations, the requisite chemicals are reacted proximate a conveyer to form large, substantially rectangular blocks which may be for example, forty inches high and six feet wide. Such blocks are normally formed in fifty foot lengths for convenient handling and storage purposes. Other lengths and sizes are also produced depending on the particular physical limitations and needs of the individual factory and its customers. Cellular foams such as polyurethanes are used in the furniture, bedding and other industries and the particular characteristics of the foam such as density, resiliency and firmness can be varied greatly depending on the required end use. As the chemical reaction of manufacture is largely exothermic, a great amount of heat is held and contained within the inner portion of the foam block as the foam surrounding the center acts as an insulator to hold the heat within. Immediately after production of a fifty foot length of an approximate four by six feet block, the outer surface temperature may fall to ambient room temperature within a few minutes whereas the center of the block which may be at over 250.degree. F., may require twenty-four hours under normal environmental conditions to reach ambient temperature. The high inner temperatures of the foam block will effect the properties of the foam, such as the density and firmness characteristics while preventing in some cases the manufacturer to ship the foam the same day as it is produced.
Others have addressed these manufacturing problems in the past as taught in U.S. Pat. No. 3,890,414 which, along with German patent No. 2,456,421 provides a method for rapidly cooling polyurethane foam blocks. U.S. Pat. No. 4,537,912 also describes a process for rapidly curing polyurethane foam. While these prior processes are helpful and beneficial under certain conditions, the foam produced thereunder lacks the degree of uniformity and firmness consistency desired and some times poor compression-set properties and accordingly, the present invention was conceived.
The physical properties of foam are generally tested per ASTM D-3574 "Standard Methods of Testing--Flexible Cellular Materials--Slab, Bonded, Molded Urethane Foams". Test methods for properties of foam, i.e. density, firmness and other qualities, are found in this publication. One of these methods (Test D) is the "Constant Deflection Compression Set Test". This test mainly deals with the recovery ability property of foam to hold its dimensional stability. Briefly the procedure calls for cutting a foam specimen that has dimensions of 50.times.50.times.25 mm. This specimen is compressed 90% of its original thickness and held compressed in this state for 22 hours between two parallel plates. Further the test specimen is placed in a mechanical convected oven that has a temperature of 70.degree..+-.2.degree. C. for this time period. The thickness of the foam specimen is accurately measured before and after the test and these measurements are calculated as a percentage of original thickness or percent loss. This percent loss is known as the Compression-Set property. Values of 10% or less are considered very good and acceptable for conventional polyether flexible polyurethane foam.
It is therefore one objective of the present invention to provide an improved process for the rapid post treatment of cellular foam to produce a foam which is uniformly consistent in density and firmness characteristics and improved compression-set properties.
It is another objective of the present invention to provide a post treatment for continuously producing foam which will provide more consistency from run to run regardless of variations in ambient temperature and humidity.
It is still another objective of the invention to provide a process for post treatment of polyurethane foam whereby a foam block is slit along two opposing side faces through the outer skin to allow recirculated air to flow through the foam to quickly and uniformly post cure and cool the foam.
It is yet another objective of the invention to provide a process for post treating cellular foam whereby the midsections of the opposing faces of the foam are slit horizontally to a depth of a fraction of an inch by adjustably fixed blades in parallel alignment.
It is also an objective of the invention to provide a process for post treating cellular foam wherein air and other gases within the foam are recirculated through the foam to improve the compression-set properties of the foam while providing a rapid post treatment.
Various other objectives and advantages of the present invention will become more apparent to those skilled in the art as the detailed description below is reviewed.